Aqueous carbon black dispersions are used in producing printing inks and are also used directly as inks, e.g., in ink-jet printers.
The ink-jet printing process is a known duplicating technology in which the printing ink is transferred in a contactless manner, that is, without contact of the printing head with the print medium. Ink drops are sprayed from a jet onto a receiving material, during which their deflection can be electronically controlled. This technology, also designated as contactless printing, is particularly suited for printing products with irregular surfaces and packages because there is a certain distance between the printing head and the matter to be printed.
The printing process is very flexible and relatively economical and is therefore also used in computer printing, e.g., in a workplace printer. The ink-jet printing process is also being increasingly used in the industrial area, e.g., in outdoor advertising. In outdoor advertising the ink must meet special requirements of resistance to light and to water. In addition, the ink components must be very finely divided so that the printer jets do not become clogged. Dyes, colorants, and, recently, even pigments are being used as color-causing substances.
Pigments have the advantage over dyes that their resistance to light is very high and that they are water-resistant. Pigments have a disadvantage compared to dyes in that they form stable dispersions with a high storage stability only by means of treatment with surface-active substances (surfactants). Pigment particles are not present in the form of primary particles but rather in the form of aggregates. Pigment aggregates are larger than soluble dyes. If pigment aggregates are not sufficiently finely dispersed they clog the jets of the printing head. In addition, large aggregates alter the light-absorption properties of the pigment black. A graying of the printing and a loss of covering power and opacity results.
A description of pigment blacks in ink-jet printer inks are found in U.S. Pat. No. 5,085,698 and U.S. Pat. No. 5,320,668. These patents describe the use of water-soluble acrylates for pigment stabilization.
The production of aqueous carbon black dispersions with carbon black having an average primary particle size of not greater than 30 nm and a DBP number of at least 75 ml/100 g is known (U.S. Pat. No. 5,538,548).
The production of aqueous carbon black dispersions using water-soluble, organic solvent and water-soluble acrylic resins is also known (U.S. Pat. No. 5,609,671).
The known aqueous carbon black dispersions have the following disadvantages:
The obtainable optical densities are comparatively low. PA1 The abrasion resistance is poor (see reference examples A, B and C). PA1 Carbon Black: 1 to 40% by weight, preferably 3 to 20% by weight, PA1 Surfactant: 1 to 30% by weight, preferably 2 to 15% by weight. PA1 Nonionic and/or anionic wetting agents can be used as surfactants. PA1 a) a cross-linked polyoxyethylene acrylic acid, and PA1 b) an alkoxyethylate, preferably a fatty acid ethoxylate, especially a fatty alcohol ethoxylate with 30 ethylene glycol units,
Therefore, the object of the invention is to produce carbon black dispersions which do not have these disadvantages.